April 10, 2011 entries

April 10, 2011

At 2:30 am PDT on April 1, 2010, the liquid hydrogen-fueled Global Observer unmanned air vehicle (UAV) "experienced a mishap" during extended duration flight testing. Personnel at Edwards Air Force base, where the Global Observer testing was based, report that it crashed. The crash occurred approximately 18 hours into its 9th test flight. The Global Observer was conducting "envelope expansion" flight testing, flying higher and for a longer duration than it had previously. Crash details are sparse, probably because AV has been ordered by the US government not to discuss the accident until after an investigation was completed. Crashes during developmental testing are not unusual, as Northrop Grumman suffered from the loss of a prototype RQ-4 Global Hawk during flights in 1999.

In my previous post, Hydrogen for 65,000 Feet, I discuss how the Global Observer was designed to fly for five to seven days, powered by liquid hydrogen, at altitudes up to 65,000 feet. Design criteria included 2.8 kilowatts (kW) of power for a 380-lb. payload, and a liquid hydrogen-fueled internal combustion engine producing about 60 kW of electricity.

AV received a US$140 million contract in September 2007 for a Joint Capability Technology Demonstration (JCTD) of the Global Observer (GO-1). Three GO-1s were planned on being built under the JCTD, jointly overseen by six U.S. government agencies. The second air vehicle is nearing completion at the AV factory. The third unit was supposed to be a backup, but it has not been discussed since the order was announced in June 2009. AV has recently stated that most of the funding for the program has been spent.

The worst part for AV is that this high-profile crash comes after another high-profile crash 8 years ago. On June 26, 2003, the NASA-funded Helios prototype UAV broke up and fell into the Pacific Ocean about 30 minutes after take-off from Kauai, in the Hawaiian islands. Helios had been quite a successful UAV, because on August 14, 2001, Helios set a world record for a winged aircraft at an altitude of 96,863 feet (29,523.8 m). Unlike Global Observer, Helios had solar cells, an electrolyzer supplied by Giner Electrochemical Systems designed to produce hydrogen and oxygen for storage, and a fuel cell fueled by the hydrogen and oxygen to produce power overnight.

"The (Helios) investigation report identified a two-part root cause of the accident:

1. Lack of adequate analysis methods led to an inaccurate risk assessment of the effects of configuration changes leading to an inappropriate decision to fly an aircraft configuration highly sensitive to disturbances.

2. Configuration changes to the aircraft, driven by programmatic and technological constraints, altered the aircraft from a spanloader to a highly point-loaded mass distribution on the same structure significantly reducing design robustness and margins of safety."

Hopefully AV can quickly get beyond this latest tragedy to continue their groundbreaking work. And hopefully the conclusions of the Global Observer investigation are not as painful as those of the Helios investigation. AV better hurry, though, as Boeing plans to fly its company-funded Phantom Eye hydrogen-fueled high-altitude, long endurance (HALE) UAV demonstrator at Edwards later this year, and Aurora Flight Sciences hopes to fly their Orion twin diesel engine-powered, five-day-endurance medium-altitude UAV this year under an Air Force-sponsored JCTD.